The field of this invention is that of electronic circuits and relates more particularly to an improved circuit board substrate and a circuit using that substrate.
Conventional electronic circuit boards are concerned with mounting silicon semiconductor devices and the like in a compact and efficient manner on printed circuit pads and pads formed on a circuit board substrate and in withdrawing heat generated during the circuit operation to improve the operating characteristics and service lives of circuit components and the reliability of component mounting and interconnection in the circuit. Such circuit boards or substrates typically include an electrically insulating layer of organic material or the like which supports a thin sheet of electrically conductive metal on one side of the insulating layer to form the circuit paths and device mounting pads on the substrate. The substrates frequently include a heat-sink layer supported in electrically insulated relation to the circuit paths and device components on an opposite side of the electrically insulating layer for withdrawing heat from the circuit and from the circuit components during circuit operation. In such conventional circuit arrangements, there is usually a substantial mismatch in coefficient of thermal expansion between the silicon semiconductor devices and the like, the circuit paths and mounting pads in the substrate, and the heat-sink layer in the substrate but the thicknesses of the substrate layers and the amount of heat generated in the circuit are such that suitable circuit operation is achieved. In addition, the electrically insulating layer in the substrate to some extent retards heat-withdrawal from the circuit and circuit components into the heat-sink layer so that the thermal expansion mismatch of the heat-sink layer is not fully effective to warp or distort the substrate so as to interfere with reliable device mounting and interconnection. However, it is now proposed to substantially increase the heat-transfer properties of the electrically insulating substrate layers for permitting substantially increased circuit component mounting densities and the like resulting in increased-generation by the circuit so that thermal coefficient of expansion mismatch between the substrate layers create difficulties in circuit operation.